The high fidelity industry has the goal of converting recorded or broadcast program material into acoustic energy in such a fashion that the apparatus is transparent to the listener, in that he perceives no substantial difference between "live," recorded or broadcast programs. One very important advance in the field has been the recognition of the advantages of stereo sound reproduction. However, experience with stereo equipment has led to the realization that merely reproducing acoustic energy in stereo format is not the ultimate in sound reproduction. As more experience is gained, further characteristics are identified which are essential to give reproduced sound the quality and feel of "live" sound. One factor whose importance has been recognized when multiple speakers are employed is phasing such that the multiple speakers truly add to, and not detract from, the resultant sound. With proper recording and reproducing techniques, an audio "image" can be created allowing the listener to locate, in three dimensions, the virtual source or sources of the sound. This effect can quite easily be destroyed by improper phasing from plural speakers, by unwanted reflections from walls, ceilings, etc. Beveridge, in U.S. Pat. No. 3,668,335, and in "Some Reflections on Sound Reproduction for the Home," advocates a system producing acoustic energy dispersing in a cylindrical wavefront. Theoretically, such an arrangement is desirable, however, implementing a system of this type is difficult. Beveridge suggests a transducer or speaker simulating a narrow slot in a wall. This should eliminate near images which can confuse the listener, reduce intensity variations and eliminate off-axis delay problems. Implementation was with a long, ribbon-like electrostatic transducer covering the entire audio range. the implementation has several significant drawbacks:
(1) the peak acoustic output capacity of the electrostatic transducer is too limited for adequate results;
(2) the electrostatic ribbon is so directional that an acoustic lens is required for adequate angular dispersion--the presence of the lens with its substantial size inhibits the effect of a narrow slot in the wall goal;
(3) the low frequency response is poor; this has led to the use of a supplementary sub-woofer.
Other attempts to improve sound quality are especially hampered in the high audio frequency range where a number of problems are present;
(1) the conventional dynamic high frequency speaker (or tweeter) is also limited in power handling capacity to about 20 watts which is inadequate for almost any application, the electrostatic alternative is even less attractive;
(2) if multiple speakers are employed in the high frequency range the transducer assembly must be arranged to minimize unwanted reflection, which is difficult since the wavelength is short; and
(3) the multiple tweeters must be arranged so as to avoid phasing inaccuracies and without their physical location or interaction producing undesirable reflections.
The prior art evidences speaker systems comprising plural dynamic transducers. One such speaker assembly includes a columnar arrangement of six 11/2 inch dome midrange drivers nominally handling the frequency range 600 Hz. to 4 kHz. placed adjacent and parallel to a 48-inch strip electromagnetic induction radiator nominally handling the frequency range 4 through 32 kHz. While this high frequency speaker assembly is capable of greater power output than is the electrostatic Beveridge arrangement, the parallel but displaced line sources consisting of the continuous ribbon electromagnetic induction tweeter and the six dome speakers can produce phase differences which tend to confuse the listener and inhibit the creation or recreation of true stereo image.
Another arrangement has an electromagnetic panel which is neither a dynamic speaker nor an electrostatic speaker. However, it is a dipole radiator, and accordingly, it cannot be positioned against a vertical surface, and must, of necessity, rely on reflections which, unless properly handled, can create the same audio confusion which destroys stereo image perception as was evident in the other prior art.
It is therefore one object of the present invention to provide a stereo speaker system which is arranged to increase stereo image perception by reducing spurious and confusing sound images. It is another object of the present invention to provide a high frequency speaker system as aforesaid, which is arranged to provide increased stereo image perception by reducing spurious and confusing sound images. It is another object of the present invention to provide a high frequency speaker assembly for use in such a system with wide dynamic range which does not degrade fidelity to achieve that range. It is a further object of the present invention to provide a high frequency speaker assembly as aforesaid, which is implemented to disperse acoustic energy as a substantially cylindrical wavefront, from floor to ceiling. It is yet another object of the present invention to provide a high frequency speaker assembly which is capable of coupling a cylindrical wavefront to a listener, and which at the same time, minimizes reflections which are capable of causing confusion in the perception of a stereo image by a listener. It is a further object of the invention to provide such high frequency speaker assembly arranged to respond to audio frequencies in a range of about 1000 Hz. and higher.